1. Field of the Invention
The present invention relates to an endoscope equipped with a shape recognition mechanism for facilitating the measurement of a shape of an object to be examined.
2. Description of the Background Art
Recently, there have been many propositions for an endoscope equipped with a shape recognition mechanism for facilitating the measurement of the shape of an object to be examined by projecting a patterned beam onto a surface of the object such that a pattern for facilitating the measurement is superposed on an image of the object taken by an imaging device of the endoscope.
A conventional endoscope equipped with the shape recognition mechanism operates as follows.
Namely, as shown in FIG. 1 for a front-viewing type endoscope, a patterned laser beam 102 is projected upon an object to be examined 103 from a beam projection unit 106 inserted into a forceps channel 107 located on a scope end surface of the scope 101, so that a line shaped pattern 104 is formed on the object 103. A reflection of the line shaped pattern 104 is then imaged by an imaging device 105 also located on the scope end surface of the scope 101 at a location separated from the forceps channel 107, along with an image of the object 103, so that the image of the object 103 with the pattern 104 superposed can be obtained. A shape of the object 103 is then analyzed on a basis of such an image with the pattern 104 superposed.
Here, as shown in FIG. 2, when a projection angle of the patterned laser beam 102 is .theta..sub.P, a receiving angle of the reflection of the pattern 104 is .theta..sub.R, a parallax Pa is given by a distance between a projection position of the patterned laser beam 102 and a center of the imaging device 105, and a length of the beam projection unit 106 protruding from the scope end surface of the scope 101 is d, a coordinate (X.sub.P, Y.sub.P, Z.sub.P) of the pattern 104 with respect to an origin located at the center of the imaging device 105 can be expressed by: EQU Z.sub.P =(Pa+d.multidot.tan .theta..sub.P)/(tan .theta..sub.P +tan .theta..sub.R) EQU X.sub.P =Zp.multidot.tan .theta..sub.R EQU Y.sub.P =Zp.multidot.tan .theta..sub.Y
where .theta..sub.Y is a receiving angle of the reflection of the pattern 104 with respect to a Y axis.
Now, such a conventional front-viewing type endoscope with a shape recognition mechanism is known to be associated with the following problems.
First of all, when the beam projection unit is provided as a permanent additional feature to an ordinary endoscope, a diameter of the scope becomes too large for practical use.
For this reason, the beam projection unit is usually inserted into the forceps channel of an ordinary endoscope as in the example of FIG. 1. However, in a conventional endoscope with a shape recognition mechanism, a position of the beam projection unit in the forceps channel could not be fixed, so that the length d and the projection angle .theta..sub.P in the above expressions could not be specified with a sufficient accuracy, which in turn affects the accuracy of the measurement of the shape.
Secondly, as shown in FIGS. 3(A) and (B), with the beam projection unit 106 inserted into the forceps channel 107, the length d and the projection angle .theta..sub.P are changed depending on a degree and a direction of bending of the scope 101, which also contributed to the inaccuracy of the measurement of the shape.
On the other hand, there is a side-viewing type endoscope with a shape recognition mechanism. In such a side-viewing type endoscope, the parallax is not limited by a size of the scope end surface of the scope, so that an accuracy of the measurment can be improved.
However, the problems described above for the front-viewing type endoscope are also pertinent for the side-viewing type endoscope.